For these types of questions: Someone can make x cakes in x days. How many cakes can someone make in x days?
You start off by finding out how many cakes he/she can make in ONE day, then multiplying it by the amount of days the question asked.
Step 1: Find out how many cakes in one day:
We can find this by dividing 42 cakes by 7 days:
42 / 7 = 6.
So Mark can make 6 cakes in 1 day.
Step 2: Find out how many cakes Mark can make in 5 days:
We can find this by multiplying the amount of cakes (6) by 5 days:
6 * 5 = 30.
So Mark can make 30 cakes in 5 days.